In the field of graphic arts, in order to improve the reproduction of continuous gradation images with halftone dot images or the reproduction of line images, image formation systems exhibiting ultrahigh-contrast (particularly, .gamma. is 10 or more) photographic characteristics are required.
An image formation system capable of obtaining ultrahigh-contrast photographic characteristics by development with a processing solution that has good storage stability has been demanded. To cope with this demand, as described in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606, and 4,311,781, a system of forming an ultrahigh-contrast negative image having a .gamma. value exceeding 10 was proposed.
In the system, a surface latent image-type silver halide photographic light-sensitive material, having added thereto a specific acylhydrazine compound, is processed with a developer containing 0.15 mol/l or more of a sulfurous acid preservative and having a pH of from 11.0 to 12.3. This new system is characterized in that silver iodobromide or silver chloroiodobromide can be used, though only silver chlorobromide having a high silver chloride content can be used in a conventional ultrahigh-contrast image formation system. Further, the new system is characterized in that a large amount of sulfurous acid preservative can be contained, and relatively good storage stability is achieved, though use of only a very small amount of sulfurous acid preservative is allowed in conventional lith developers.
In European Unexamined Patent Publication (EP) 0 208 514A, JP-A-61-223734 ("JP-A" means unexamined published Japanese patent application), and JP-A-63-46437, high-contrast photographic light-sensitive materials containing two types of silver halide grains, and further containing a hydrazine derivative, are described. These light-sensitive materials are processed with developers having a high pH of about 11.5. However, developers having a pH of 11 or more are prone to air oxidation, and they are unstable and not endurable in use or storage for a long period of time. In addition, since attention must be given to both handling and processing of a waste solution of the developers, a solution having a high pH is unfavorable from an ecological viewpoint. Rather, a means for subjecting to development a silver halide photographic light-sensitive material containing a hydrazine compound with a developer having a lower pH, is preferred in forming a high-contrast image.
On the other hand, when the pH of the developer is low, the contrast-increasing effect induced by the hydrazine derivative is so lowered that a high-contrast image cannot be obtained. In order to accelerate the contrast-increasing effect, development of hydrazine derivatives having higher activity and nucleation accelerators has been attempted. However, use of these compounds, on some occasion, deteriorates long-term storage stability of the light-sensitive material.
JP-A-4-331951 describes, in its claim, a high-contrast light-sensitive material that comprises a hydrazine derivative and silver halide grains that have been subjected to color sensitization in higher concentration of a dye per the surface area of a silver halide grain, than the other silver halide grains do. Further, British unexamined patent publication (GB-A) 9407599 describes, in its claim, a high-contrast light-sensitive material that comprises silver halide grains spectrally sensitized by an undetachable sensitizing dye, and silver halide grains not spectrally sensitized, and further a hydrazine derivative. In both cases, the spectrally sensitized light-sensitive grains and the spectrally unsensitized non-light-sensitive grains contribute to a silver image formed by image-wise exposure and development, due to the presence of the hydrazine derivative, thereby achieving a reduction in amount of the sensitizing dye and improvement on residual color, while maintaining both high sensitivity and high density. However, the former case had a problem that, when photographic emulsions were left standing for a long time in a mixed state, the distribution of the dye in the mixed emulsions became homogeneous, so that a reduction in sensitivity was caused. Further, in the latter case, because the dye to be used was restricted to an undesorbable dye, which was hardly desorbed from a photographic emulsion, satisfactory results on residual color could not be achieved. Further, these patent publications do not disclose anything about the differences of grain formation methods for emulsions to be mixed.